Such a wheelchair is known, for example, from U.S. Pat. No. 5,884,928 A.
DE 10 2009 049 536 A1 makes known a wheelchair where the seat is adjustable in height and inclination. The seat frame serves for receiving the seat shells or orthopedic seats (which are to be understood as synonymous in the following text) and together with said seat shells forms the seat system for persons who are unable to sit independently as a result of a disability. Seat shells and orthopedic seats are produced individually for said persons because, as a rule, they have serious physical limitations. The seat system is to compensate possibly for existing deformations of the skeleton (for example aligning the pelvis horizontally). As in the case of all sitting persons, the body weight is absorbed to a great extent in the ischium region. In the case of persons with movement limitations, the continual pressure load can result in decubitus. To reduce the risk of decubitus, the body weight has to be distributed over a larger support surface. This is achieved as a result of the inclination of the seat system, the inclination of the seat system being adjusted as a result of an inclination of the seat frame.
In particular when the adjustable region of the inclination is large, for example up to 50°, and the weight of the person utilizing the seat system is heavy, it is necessary for the actuating forces in the case of a change in inclination to be low in order to make the optimum adjustment easier for a carer. The simplest way to reduce the actuating forces is to displace the rotational axis into the common center of gravity of the seat system and the user (patient).
In the case of the wheelchair known from US 2009/0045599 A1, the rotational axis of the seat system is provided in the vicinity of the center of gravity of the user in order to realize angles of inclination of the seat system of up to 50°. Said wheelchair is structurally very expensive. The adjustability of the seat system or of the seat frame can certainly be made easier by means of a telescopic cylinder, the mechanism connected thereto makes the wheelchair more expensive, increases its weight, as a result of which the handling characteristics are impaired, and it is additionally susceptible to faults.
DE 89 08 374 makes known an interchangeable device for a seat which can be connected to an underframe. Said underframe can be a baby-stroller or a wheelchair for children. To this end, the seat is mountable so as to be rotated by 180° such that the line of vision of the person received by the seat is either directed forward or rearward. The seat is fastened on the underframe by means of an adjustable safety lock.
U.S. Pat. No. 2,986,200 discloses a wheelchair where the seat is able to be pivoted from a vertical into a horizontal position in order to be able to transport disabled persons not only sitting but also lying. The seat can assume the function of a bed in the horizontal position.
DE 10 2004 045 388 B4 makes known an electric wheelchair where the seat is adjustable automatically in its inclination such that the seat always remains in the horizontal even when going up and down. Two guide rails, which are mounted in each case in four rollers which are fixed to the chassis, are fastened to the driver's seat for this purpose. If the vehicle travels uphill, the seat is pivoted about a virtual pivot point which is situated in the vicinity of the mass pivot point of a person sitting on the seat.